Display device comprising first and second light guide plates having recessed patterns and flat surfaces that face each other to form first and second empty spaces wherein the second empty space is narrower than the first empty space

ABSTRACT

A display device includes a liquid crystal display panel that varies a phase of polarized light via liquid crystal molecules, wherein second recessed patterns of a second light guide plate are directly faced with first recessed patterns of a first light guide plate to form a first empty space, and wherein first flat surfaces of the first light guide plate are directly faced with second flat surfaces of the second light guide plate to form a second empty space narrower than the first empty space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of co-pending U.S. application Ser. No.12/879,549 filed Sep. 10, 2010, which claims priority to Korean PatentApplication No. 10-2009-0087442, filed on Sep. 16, 2009. The contents ofall of these applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to a display device, and more particularly to atransparent display device with a liquid crystal display (LCD) panel.

2. Discussion of the Related Art

Most recently, transparent display devices are actively being researchedwhich allow not only an image to be displayed thereon but also allowsobjects at their rear side to be viewed. These transparent displaydevices can be ordinarily realized employing any one of an organic lightemission panel and a plasma display panel which use self-generatedlight.

However, the transparent display devices cannot ordinarily be realizedemploying an LCD panel which does not self generate light and must uselight applied from the rear side. This results from the fact that anopaque backlight assembly must be disposed at the rear side of the LCDpanel and polarizing plates for controlling the penetration of lightmust be attached to the front and rear surfaces of the LCD panel. Morespecifically, the polarizing plates on the front and rear surface of theLCD panel allow light to pass through them when a liquid crystalmaterial within the LCD panel is driven. On the contrary, when theliquid crystal material is not driven, the polarizing plates are in anopaque state. Due to this, it is impossible to implement the transparentdisplay device using the LCD panel.

Nevertheless, transparent display devices can be applied to the frontglasses of vehicles, household glasses, and so on, in order to providedesired information to users. Also, it is evident that the possibilityof applying the transparent display device in a variety of fields willrapidly increase. Moreover, since the LCD panel provides a wideviewing-angle, a high brightness, a high contrast ratio, and a fullcolor display, it is very necessary to develop a transparent displaydevice with the LCD panel.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the invention are directed to a transparentdisplay device that substantially obviates one or more of problems dueto the limitations and disadvantages of the related art.

An object of the invention is to provide a transparent display devicethat is adapted to selectively drive an LCD panel in transparent andopaque modes.

Additional features and advantages of the embodiments of the inventionwill be set forth in the description which follows, and in part will beapparent from the description, or may be learned by practice of theinvention. The advantages of the embodiments will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

According to an embodiment of the invention, a display device includes aliquid crystal display panel that varies a phase of polarized light vialiquid crystal molecules, and having first and second polarizing platesrespectively disposed on opposite sides of the liquid crystal displaypanel; a first light guide plate including a surface having a pluralityof recessed patterns, to reflect light input through a side surface ofthe first light guide plate, and to output two-dimensional light towardsthe liquid crystal display panel; and a second light guide plateincluding a surface having a plurality of recessed patterns, theplurality of recessed patterns of the second guide plate facing theplurality of recessed patterns of the first light guide plate.

According to another embodiment of the invention, a display deviceincludes a liquid crystal display panel that varies a phase of polarizedlight via liquid crystal molecules; a first light guide plate includinga surface having a plurality of recessed patterns, and a firstpolarizing plate disposed at an incident surface of the first lightplate; a second light guide plate including a surface having a pluralityof recessed patterns, the plurality of recessed patterns of the secondguide plate facing the plurality of recessed patterns of the first lightguide plate; and a second polarizing plate disposed on the liquidcrystal display panel.

According to another embodiment of the invention, a display deviceincludes a liquid crystal display panel that varies a phase of polarizedlight via liquid crystal molecules; a first light guide plate includinga planar first surface, and a second surface having a plurality ofrecessed patterns; and a second light guide plate including a planarfirst surface, and a second surface having a plurality of recessedpatterns, wherein amounts of light respectively emitted from the firstand second surfaces of the first light guide plate are different, andamounts of light respectively emitted from the first and second surfacesof the second light guide plate are different.

Other systems, methods, features and advantages will be, or will become,apparent to one with skill in the art upon examination of the followingfigures and detailed description. It is intended that all suchadditional systems, methods, features and advantages be included withinthis description, be within the scope of the invention, and be protectedby the following claims. Nothing in this section should be taken as alimitation on those claims. Further aspects and advantages are discussedbelow in conjunction with the embodiments. It is to be understood thatboth the foregoing general description and the following detaileddescription of the present disclosure are exemplary and explanatory andare intended to provide further explanation of the disclosure asclaimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the embodiments and are incorporated in and constitutea part of this application, illustrate embodiment(s) of the inventionand together with the description serve to explain the disclosure. Inthe drawings:

FIG. 1 is a perspective view showing a transparent display deviceaccording to a first embodiment of the invention;

FIGS. 2A and 2B are cross-sectional views illustrating the transparentdisplay device of FIG. 1 driven in transparent and opaque modes,respectively;

FIG. 3 is a waveform diagram sequentially illustrating lights fromrespective light sources being polarized in the transparent displaydevice of FIG. 1;

FIGS. 4A and 4B are views showing the transparent display device of FIG.1 driven in the transparent and opaque modes, respectively;

FIG. 5 is a perspective view showing of a transparent display deviceaccording to a second embodiment of the invention;

FIGS. 6A and 6B are cross-sectional views illustrating the transparentdisplay device of FIG. 5 driven in transparent and opaque modes,respectively;

FIG. 7 is a waveform diagram sequentially illustrating lights fromrespective light sources being polarized in the transparent displaydevice of FIG. 5;

FIG. 8 is a cross-sectional view showing a transparent display deviceaccording to a third embodiment of the invention; and

FIG. 9 is a cross-sectional view showing a transparent display deviceaccording to a fourth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. These embodiments introduced hereinafter are provided asexamples in order to convey their spirits to the ordinary skilled personin the art. Therefore, these embodiments may be embodied in a differentform, so are not limited to these embodiments described here. Also, thesize and thickness of the device might be expressed to be exaggeratedfor the sake of convenience in the drawings. Wherever possible, the samereference numbers will be used throughout this disclosure including thedrawings to refer to the same or like parts.

Transparent display devices according to the example embodiments of theinvention will now be explained in detail with reference to the attacheddrawings.

FIG. 1 is a perspective view showing a transparent display deviceaccording to a first embodiment of the invention. As shown in FIG. 1,the transparent display device according to the first embodiment of theinvention includes an LCD panel 10 configured to display images, andfirst and second light sources 40 and 41 each configured to emit light.The transparent display device further includes first and second lightguide plates 20 a and 20 b each configured to derive two dimensionallight from light which is generated in the respective one of the firstand second light sources 40 and 41, and first and second polarizingplates 11 a and 11 b disposed above and under the LCD panel 10 and eachconfigured to polarize light. Both the first and second light guideplates 20 a and 20 are formed to have a cross-section of a planar shape.

The LCD panel 10 is configured with a thin film transistor (TFT) arraysubstrate and a color filter substrate which are combined with a liquidcrystal layer being between the TFT array and color filter substrates.The TFT array substrate includes a plurality of TFTs, pluralities ofgate and data lines configured to cross each other and to define pixelregions, and a plurality of pixel electrodes arranged in the pixelregions. The color filter substrate includes a latticed black matrixused to shield light, and red, green and blue color filter layers formedbetween the black matrix.

The first and second light sources 40 and 41 are disposed to face firstand second incident surfaces 31 and 32 of the first and second lightguide plates 20 a and 20 b, respectively. Each of the first and secondlight sources 40 and 41 can include one of a lamp, such as a coldcathode fluorescent lamp (CCFL), an external electrode fluorescent lamp(EEFL), or others, and a light emission diode array. The light emissiondiode array can include either red, green, and blue light emissiondiodes or a plurality of white light emission diodes. Alternatively, thelight emission diode array can include light emission diode packageseach configured with red, green, and blue light emission diodes whichare combined in a single package. The light emission diode array mayalso include a ultra-violet light emission diode. Such first and secondlight sources 40 and 41 emit visible light which includes first andsecond polarization components (for example, vertical and horizontalpolarization components).

The first light guide plate 20 a with the first incident surface 31facing the first light source 40 is configured to include a plurality ofrecessed patterns 22 formed in its lower surface (the surface facing thesecond light guide plate 20 b). The plurality of recessed patterns 22enables light entered from the first light source 40 to be totallyreflected, refracted, and scattered before converted intotwo-dimensional light progressing toward the upper surface of the firstlight guide plate 20 a facing the LCD panel 10. In other words, theplurality of recessed patterns 22 functions to derive two-dimensionallight from light generated in the first light source 40.

Such recessed patterns 22 can be formed by irradiating laser light onthe lower surface of the first light guide plate 20 a and the uppersurface of the second light guide plate 20 b using a separate mask withthe same patterns as the recessed patterns. In this instance, theirradiating energy and period of laser light depend upon thespecifications of a transparent display device, for example, the sizeand kind of the LCD panel 10. Alternatively, the recessed patterns 22can be formed through any one among an etching process, a printingprocess, a prominence depressing process, and others. Also, thetransparency and brightness of the transparent display device are variedalong the size of the recessed pattern 22 and the distance between therecessed patterns 22. As such, in order to provide desired transparencyand brightness, it is necessary to adjust the size of the recessedpattern 22 and the distance between the recessed patterns 22. Inembodiments of the invention, the recessed patterns 22 may have variousshapes, such as hemispherical, columnar, cone, and so on. Further, a mixof different shaped recessed patterns may be formed on the relevantsurfaces of the first and second light guide plates 20 a and 20 b, forexample.

Similarly, the second light guide plate 20 b with the second incidentsurface 32 facing the second light source 41 is configured to include aplurality of recessed patterns 22 formed in its upper surface (thesurface facing the first light guide plate 20 a). The plurality ofrecessed patterns 22 enables light entered from the second light source41 to be totally reflected, refracted, and scattered before beingconverted into two-dimensional light that progresses toward the lowersurface of the second light guide plate 20 b, i.e., in an oppositedirection to the LCD panel 10. In other words, the plurality of recessedpatterns 22 functions to derive two-dimensional light from lightgenerated in the second light source 41.

However, each of the first and second light guide plates 20 a and 20 ballows about 30% of light to be output toward the surface where therecessed patterns 22 are formed. More specifically, about 70% of theconverted two-dimensional light is output toward the surface not havingthe recessed patterns 22, and about 30% of the converted two-dimensionallight is output toward the surface having the recessed patterns 22. Thetwo-dimensional light output from each of the first and second lightguide plates 20 a and 20 b is non-polarized light.

Although the plurality of recessed patterns 22 is formed in the uppersurface of the second light guide plate 20 b, the recessed patterns 22can be formed in the lower surface of the second light guide plate 20 blike those of the first light guide plate 20 a. As shown in theembodiment of FIG. 1, the first and second light guide plates 20 a and20 b can be disposed to allow the surfaces each provided with therecessed patterns 22 to face each other.

The transparent display device according to the invention can realize atransparent display, which projects objects at its rear side, using onlythe first light guide plate 20 a, because of the lack of a reflectivesheet. On the other hand, the transparent display device of theinvention further using two-dimensional light derived by the secondlight guide plate 20 b can realize a transparent display with animproved definition (a higher definition that that of the formerinstance).

More specifically, If light enters the second light guide plate 20 b,70% of two-dimensional light progresses in a downward direction of thesecond light guide plate 20 b, but 30% of two-dimensional lightprogresses in a upward direction of the second light guide plate 20 b.The downwardly progressing two-dimensional light is irradiated toobjects which are positioned under the second light guide plate 20 b.The upwardly progressing two-dimensional light is input to the LCD panel10 via the upper surface of the second light guide plate 20 b with therecessed patterns 22 in such manner as to have a phase difference withrespect to two-dimensional light which is converted by the first lightguide plate 20 a. As such, the objects at the rear of the transparentdisplay device can be more definitively viewed to a user.

In this transparent mode, two-dimensional light derived by the firstlight guide plate 20 a is used for displaying an image on the LCD panel10, two-dimensional light derived by the second light guide plate 20 bis used for distorting a white light component of the image displayed onthe LCD panel 10. Due to this, light reflected by the objects at therear of the second light guide plate 20 b is projected to the eyes of auser through the LCD panel 10. If an image including only black colorcomponents is displayed on the LCD panel 10, all of lights applied fromthe rear of the LCD panel 10 are thoroughly shielded by the first andsecond polarizing plates 11 a and 11 b. On the contrary, when an imagewith the brightness of above a fixed degree (or a fixed gray level) isdisplayed on the LCD panel 10, two-dimensional light derived by thefirst light guide plate 20 a is transmitted through the LCD panel 10.Then, white light or high brightness light of the image is distorted bylight derived by the second light guide plate 20 b. As such, lightreflected by the objects at the rear of the LCD panel 10 is transmittedthrough the LCD panel 10 and the first and second polarizing plates 11 aand 11 b.

In accordance therewith, the second light guide plate 20 b can be usedto control the LCD panel 10 to be driven in either a transparent mode (afirst mode) or an opaque mode (a second mode). In embodiments of theinvention, reference to a transparent mode indicates that light isseparately provided to the second light guide plate 20 b, whilereference to an opaque mode indicates that light is not separatelyprovided to the second light guide plate 20 a. In embodiments of theinvention, when the light is separately provided to the second lightguide plate 20 b, an observer looking at the LCD panel 10 is better ableto see a scene or an object that is positioned at or beyond an oppositeside of the LCD panel 10 with respect to the observer. Accordingly,there is an improvement in brightness, clarity, etc, of the scene orobject relative to when the light is not separately provided to thesecond light guide plate 20 b.

In detail, almost all incident light to the second light guide plate 20b is output in the form of two-dimensional light which progresses in thelower surface direction of the second light guide plate 20 b, when thesecond light source 41 is turned-on (or activated). The downwardprogressing two-dimensional light is irradiated to objects positioned atthe rear of the display device. On the other hand, the rest of theincident light corresponding to 30% is output in the form oftwo-dimensional light which progresses toward the upper surface of thesecond light guide plate 20 b provided with the recessed patterns 22.Two-dimensional lights progressing from the first and second light guideplates 20 a and 20 b toward the LCD panel 10 have a fixed phasedifference from each other due to a difference between their travelingdistances. Also, two-dimensional light derived by the second light guideplate 20 b distorts the white light components of an image while itpasses through the second polarizing plate 11 b, LCD panel 10 and firstpolarizing plate 11 a. To this end, the light reflected by objects atthe rear of the second light guide plate 20 b can be transmitted throughthe second polarizing plate 11 b, LCD panel 10 and first polarizingplate 11 a. Therefore, the objects positioned at the rear of the secondlight guide plate 20 b can be projected while images are displayed onthe LCD panel 10. In other words, the LCD panel 10 is driven in thetransparent mode. The second light source 41 is preferably configured toemit 1.3˜1.5 times brighter light than that of the first light source40.

On the contrary, when the second light source 41 is turned-off (ornon-activated), the second light guide plate 20 b can not provideindependent light including the first and second polarizationcomponents. As such, the LCD panel 10 is driven in the opaque mode. Inother words, the turned-off second light source 41 forces the LCD panel10 to enter the opaque mode, so that an image is displayed on the LCDpanel 10 by only two-dimensional light derived in the first light guideplate 40.

FIGS. 2A and 2B are cross-sectional views illustrating the transparentdisplay device of FIG. 1 driven in transparent and opaque modes,respectively. FIG. 3 is a waveform diagram sequentially illustratinglights from light sources being polarized in the transparent displaydevice of FIG. 1. As shown in FIGS. 2A and 2B, the transparent displaydevice of the first embodiment allows the LCD panel 10 to be driven ineither a transparent display mode or an opaque display mode.

First, if the transparent display device of the first embodiment isdriven in the transparent mode, the first and second light sources 40and 41 disposed to face the incident surfaces of the first and secondlight guide plates 20 a and 20 b are in a turned-on state, as shown inFIG. 2A. The operation of the transparent display device in thetransparent mode will be explained in detail with reference to FIGS. 2Aand 3.

While the first light source 40 disposed to face the incident surface ofthe first light guide plate 20 a is in the turned-on state, lightprogresses from the first light source 40 to the inner side of the firstlight guide plate 20 a through the incident surface of the first lightguide plate 20 a. At this time, the light traveling within the firstlight guide plate 20 a includes the first and second polarizationcomponents and is non-polarized light. The light with the first andsecond polarization components is entirely (totally) reflected (morespecifically, are reflected, refracted, and scattered) by the recessedpatterns 22 formed at the lower surface of the first light guide plate20 a and converted into two-dimensional light which progresses towardthe LCD panel 10 disposed above the first light guide plate 20 a.

Similarly, light entered from the turned-on second light source 41 intothe second light guide plate 20 b is entirely (or totally) reflected bythe recessed patterns 22, which are formed at the upper surface of thesecond light guide plate 20 b, and output in the form of two-dimensionallight progressing toward the downward direction of the second lightguide plate 20 b. At this time, about ⅓ of the two-dimensional lightconverted by the recessed patterns 22 of the second light guide plate 20b is output toward the first light guide plate 20 a. Fainttwo-dimensional-light output from the second light guide plate 20 b ismixed with two-dimensional light derived in the first light guide plate20 a in a space between the second polarizing plate 11 b and the firstlight guide plate 20 a. Two-dimensional lights derived by the first andsecond light guide plates 20 a and 20 b have a fixed phase differencefrom each other due to a difference between their traveling paths(distances).

The mixed two-dimensional lights each having the first and secondpolarization components are polarized in the second polarizing plate 111b and then are transmitted through the LCD panel 10 and the firstpolarizing plate 11 a. The transmitted two-dimensional light is used toform white image components of an image displayed on the LCD panel 10.This white light is basically configured with the two-dimensional lightconverted by the first light guide plate 20 a. However, the white lightfurther includes two-dimensional light converted by the second lightguide plate 20 b in the transparent mode. At this time, the white lightis distorted by two-dimensional light derived in the second light guideplate 20 b. The distortion of the white image components displayed onthe LCD panel 10 allow non-polarized light components, which arereflected by the objects at the rear of the LCD panel 10, to betransmitted through the first and second polarizing plates 11 a and 11 band LCD panel 10. Accordingly, the objects positioned at the rear of theLCD panel 10 can be viewed to the eyes of a user.

In this manner, two-dimensional light converted by the second lightguide plate 20 b is transferred to users through the LCD panel 10. Assuch, the objects positioned at the rear of the transparent displaydevice can be viewed to the users. Two-dimensional lights progressingupwardly and downwardly from the second light guide plate 20 b enablethe objects at the rear of the transparent display device to be moredefinitively viewed to the users. In other words, the LCD panel 10 notonly displays an image using two-dimensional light derived by the firstlight guide plate 20 a under it, but also projects the objectspositioned at the rear of the second light guide plate 20 b usingtwo-dimensional light derived by the second light guide plate 20 b.

Secondly, when the transparent display device of the first embodiment isdriven in the opaque mode, the second light source 41 disposed to facethe incident surface of the second light guide plate 20 b is in aturned-off state, as shown in FIG. 2B. Therefore, the LCD panel 10 candisplay an image using only two-dimensional light derived by the firstlight source 40 and the first light guide plate 20 a. In this opaquemode, the transparent display device is driven in the same manner as theimage display operation of an ordinary LCD device

When the LCD panel 10 is driven in the transparent mode, the transparentdisplay device has a light variation as shown in FIG. 3. As both thefirst and second light sources 40 and 41 are turned-on in thetransparent mode, the first and second light sources 40 and 41 emitnon-polarized light including the first and second polarizationcomponents. As such, two-dimensional light output from the upper surfaceof the first light guide plate 20 a includes two kinds of non-polarizedlights. However, the non-polarized two-dimensional lights have a fixedphase difference from each other because they are disposed at differentpositions from each other.

Non-polarized two-dimensional lights converted by the first light guideplates 20 a and 20 b are polarized and mixed with each other whilepassing through the second polarizing plate 11 b. Also, the polarizedand mixed two-dimensional lights interfere with each other. Suchpolarized and mixed two-dimensional lights enable white image componentsdisplayed on the LCD panel 10 to be distorted when they pass through theLCD panel 10 and first polarizing plate 11 a. In accordance therewith,light reflected by the objects positioned at the rear of the secondlight guide plate 20 b can be projected. In order to project moredefinitively the objects positioned at the rear of the display device,the second light source 41 included in the first embodiment is designedto emit 1.3˜1.5 times brighter light than that of the first light source40.

FIGS. 4A and 4B are views showing the transparent display device of FIG.1 driven in the transparent and opaque modes, respectively.

Both the first and second light sources 40 and 41 are in the turned-onstate in the transparent mode. In this instance, the objects positionedat the rear of the display device is viewed to users by lightprogressing from the second light guide plate 20 b toward the LCD panel10, as shown in FIG. 4A.

On the contrary, the second light source 41 is in the turned-off stateand the first light source 40 is in the turned-on state, in the opaquemode. As such, two-dimensional light is not derived by the second lightguide plate 20 b. Therefore, the LCD panel 10 displays an image usingonly two-dimensional light converted in the first light guide plate 20a. In other words, the display device can display only an image withoutor weakly projecting the objects positioned at its rear side, as shownin FIG. 4B. As a result, the objects positioned at the rear of thedisplay device are not viewed or less clearly viewed to the eyes of auser. More specifically, because the second light guide plate 20 b isdisposed under the first light guide plate 20 a, the objects positionedat the rear of the display device are thoroughly or partially shieldedin the opaque mode.

FIG. 5 is a perspective view showing a transparent display deviceaccording to a second embodiment of the invention.

Referring to FIG. 5, the transparent display device according to thesecond embodiment of the invention includes an LCD panel 110 configuredto display images, and first and second light sources 140 and 141 eachconfigured to emit light. The transparent display device furtherincludes first and second light guide plates 120 a and 120 b eachconfigured to derive two dimensional light from light which is generatedin the respective one of the first and second light sources 140 and 141,a first polarizing plate 1111 a disposed on an incident surface 31(first incident surface) of the first light guide plate 120 a andconfigured to polarize light, and a second polarizing plate 111 bdisposed above the LCD panel 110 and configured to polarize light. Thereference number of “32” indicates an incident surface (second incidentsurface) of the second light guide plate 120 b.

The LCD panel 110 is configured with a TFT array substrate and a colorfilter substrate which are combined with a liquid crystal layer beingbetween the TFT array and color filter substrates. The TFT arraysubstrate includes a plurality of TFTs, pluralities of gate and datalines configured to cross each other and to define pixel regions, and aplurality of pixel electrodes arranged in the pixel regions. The colorfilter substrate includes a black matrix used to shield light, and red,green and blue color filter layers formed between the black matrix.

The first light source 140 is disposed to face the first polarizingplate 111 a on the first incident surface 31 of the first light guideplate 120 a. The second light source 141 is disposed to face the secondincident surface 32 of the second light guide plate 120 b. The first andsecond light sources 140 and 141 may be configured in the same manner asthose described in the first embodiment of FIG. 1.

The first and second light guide plates 120 a and 120 b and the recessedpatterns 122 are formed in the same structures as those described in thefirst embodiment. Also, the first and second light guide plates 120 aand 120 b and the recessed patterns 122 have the same functions as thosedescribed in the first embodiment. Therefore, the detailed descriptionof the first and second light guide plates 122 a and 122 b and recessedpatterns 122 will be omitted.

FIGS. 6A and 6B are cross-sectional views illustrating the transparentdisplay device of FIG. 5 driven in transparent and opaque modes,respectively. FIG. 7 is a waveform diagram sequentially illustratinglights from light sources being polarized in the transparent displaydevice of FIG. 5. As shown in FIGS. 6A and 6B, the transparent displaydevice of the second embodiment allows the LCD panel 110 to display animage in transparent and opaque modes.

First, if the transparent display device of the second embodiment isdriven in the transparent mode, the second light sources 141 disposed toface the incident surface 32 of the second light guide plates 120 b isin a turned-on state. Also, the first light source 140 disposed to facethe first polarizing plate 111 a on the incident surface 31 of the firstlight guide plate 120 a is in the turned-on state. The operation of thetransparent display device in the transparent mode will be explained indetail with reference to FIGS. 6A and 7.

As the first light source 140 disposed to face the first polarizingplate 111 a on the incident surface 31 of the first light guide plate120 a is in the turned-on state, light including the first and secondpolarization components is emitted from the first light source 140 andpolarized by the first polarizing plate 111 a. The light emitted in thefirst light source 140 includes both the first and second polarizationcomponents, but the polarized light output from the first polarizingplate 111 a includes only the first polarization component.

At the same time, light entered from the turned-on second light source141 into the second light guide plate 120 b is output in the form ofnon-polarized two-dimensional light which progresses in the downwarddirection of the second light guide plate 120 b and toward the firstlight guide plate 120 a. In this instance, the amount of two-dimensionallight progressing toward the first light guide plate 120 a correspondsto about ⅓ (i.e., 30%) of that of two dimensional light progressing inthe downward direction of the second light guide plate 120 b. In thisinstance, it is preferable, though not required, for the second lightsource 141 to emit light of the same brightness as light emitted fromthe first light source 140.

As such, two-dimensional light passing through the upper surface of thefirst light guide plate 120 a includes two-dimensional light with onlythe first polarization component polarized by the first polarizing plate111 a and two-dimensional light with both the first and secondpolarization components converted in the second light guide plate 120 b.Among two-dimensional lights, the polarized two-dimensional lightconverted by the first light guide plate 120 a is used to display animage on the LCD panel 110. On the other hand, the non-polarizedtwo-dimensional light of the first and second polarization components,which is converted by the second light guide plate 120 b, is used toproject the object positioned at the rear of the display device byinterfering with the polarized two-dimensional light, which is convertedby the first light guide plate 120 a. Consequently, because thepolarized and non-polarized two-dimensional lights interfere with eachother when they are mixed with each other, it can be substantiallyrealized the transparent mode which enables not only an image to bedisplayed on the LCD panel 110 but also objects positioned at the rearside of the display device to be projected.

When the transparent display device of the second embodiment is drivenin the opaque mode, the second light source 141 is in the turned-offstate. As such, the LCD panel 110 can display an image using onlytwo-dimensional light of first polarization component which is derivedby the first light source 140 and the first light guide plate 120 a.Therefore, the objects positioned at the rear of the second light guideplate 120 b are not displayed to users. In this opaque mode, thetransparent display device is driven in the same manner as the imagedisplay operation of an ordinary LCD device.

FIG. 8 is a cross-sectional view showing a transparent display deviceaccording to a third embodiment of the invention, and FIG. 9 is across-sectional view showing a transparent display device according to afourth embodiment of the invention.

The transparent display device of the third embodiment shown in FIG. 8has a structure modified from that of the first embodiment. Thetransparent display device of the third embodiment performs the sameoperation as that of the first embodiment in the transparent and opaquemodes. Also, the transparent display device of the fourth embodimentshown in FIG. 9 has a structure modified from that of the secondembodiment. The transparent display device of the fourth embodimentperforms the same operation as that of the second embodiment in thetransparent and opaque modes. Therefore, the descriptions of the thirdand fourth embodiments overlapping those of the first and secondembodiments will be omitted.

Referring to FIG. 8, the transparent display device includes first andsecond polarizing plates 11 a and 11 b that are disposed to face an LCDpanel 10 disposed in between the two polarizing plates 11 a and 11 b.The transparent display device further includes a first light guideplate 220 a disposed under the second polarizing plate 11 b and formedto have a cross-section of a wedge shape and a surface with recessedpatterns 222, and a second light guide plate 220 b formed to have across-section of the wedge shape and a surface with the recessedpatterns 222 which faces the recessed pattern surface of the first lightguide 220 a. Furthermore, the transparent display device includes afirst light source 40 disposed to face an incident surface (firstincident surface) 231 of the first light guide plate 220 a, and a secondlight source 41 disposed to face an incident surface (second incidentsurface) 232 of the second light guide plate 220 b.

The first light guide plate 220 a is configured to have an edge portionthat includes the first incident surface 231 to have the thickestthickness. In detail, the first light guide plate 220 a is formed toprogressively have a thinner thickness further away from the firstincident surface 231. Similarly, the second light guide plate 220 b isconfigured to have an edge portion that includes the second incidentsurface 232 to have the thickest thickness. In other words, the secondlight guide plate 220 b is formed to progressively have a thinnerthickness further away from the second incident surface 232.

The pluralities of recessed patterns 222 are formed in a lower surfaceof the first light guide plate 220 a and an upper surface of the secondlight guide plate 220 b, respectively. The recessed patterns 222 formedin the first light guide plate 220 a are arranged to face the recessedpatterns 222 formed in the second light guide plate 220 b.

Also, the first incident surface 231 of the first light guide plate 220a and the second incident surface 232 of the second light guide plate220 b are disposed at opposite directions to each other. In other words,the first and second incident surfaces 231 and 232 are disposed to faceeach other with respect to a middle portion of the bodies of the lightguide plates 220 a and 220 b.

As such, the first and second light sources 40 and 41 are disposed toface each other in the center of the first and second light guide plates220 a and 220 b. The second light source 41 is configured to emit1.3˜1.5 times brighter light than that emitted from the first lightsource 40, like the second light source 41 included in the transparentdisplay device according to the first embodiment.

In this manner, the first and second light guide plates 220 a and 220 bare formed in the wedge shape. As such, the thickest portion of thefirst light guide plate 220 a can be positioned to overlap the thinnestportion of the second light guide plate 220 b and vice versa. Therefore,a slimed transparent display device can be implemented.

As shown in FIG. 9, the transparent display device of the fourthembodiment modified from that of the second embodiment, and includes anLCD panel 110, and first and second light guide plates 220 a and 220 bdisposed under the LCD panel 110. The transparent display device furtherincludes a first polarizing plate 111 a attached to a first incidentsurface of the first light guide plate, and a second polarizing plate111 b disposed above the LCD panel 110.

The first and second light guide plate 220 a and 220 b are formed in thecross-sectional structures of a wedge shape. In detail, the thicknessesof the first and second light guide plates 220 a and 220 b progressivelybecome thinner further away from the respective incident surfaces 231and 232. Also, the first and second incident surfaces 231 and 232 of thefirst and second light guide plates 220 a and 220 b are disposed to faceeach other with respect to a middle portion of the bodies of the firstand second light guide plates 220 a and 220 b, like the first and secondincident surfaces 231 and 232 described in the transparent display ofFIG. 8.

Furthermore, the transparent display device of the fourth embodimentincludes first and second light sources 140 and 141 disposed to face thefirst and second incident surfaces of the first and second light guideplates 220 a and 220 b. The first and second light sources are disposedon the opposite sides to each other with respect to a middle portion ofthe light guide lights 220 a and 220 b, respectively.

Such a transparent display device according to the fourth embodiment isdriven in the same manner as that of the second embodiment in thetransparent and opaque modes. Therefore, the operations of thetransparent display device according to the fourth embodiment will beomitted.

As described above, the transparent display devices according to theinvention enable objects positioned at their rear sides to beselectively viewed or not viewed by users while images are displayed. Assuch, the transparent display devices according to the invention areimplemented using an LCD panel which is normally not realized as atransparent display. Therefore, the applicable field of the LCD panelcan be expanded. Furthermore, a variety of content images can bedisplayed using the LCD panel.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A display device, comprising: a liquid crystaldisplay panel that varies a phase of polarized light via liquid crystalmolecules; a first light guide plate including an incident surface, anupper surface and a bottom surface, the bottom surface having aplurality of first recessed patterns and first flat surfaces disposedbetween the first recessed patterns; a second light guide plateincluding an upper surface and a bottom surface, the upper surfacehaving a plurality of second recessed patterns and second flat surfacesdisposed between the second recessed patterns; a first polarizing plateon the incident surface of the first light guide plate; and a secondpolarizing plate disposed on the liquid crystal display panel, whereinthe second recessed patterns of the second light guide plate aredirectly faced with the first recessed patterns of the first light guideplate to form a first empty space, and wherein the first flat surfacesof the first light guide plate are directly faced with the second flatsurfaces of the second light guide plate to form a second empty spacenarrower than the first empty space.
 2. The display device as claimed inclaim 1, wherein light input to the incident surface of the first lightguide plate is used to display an image on the liquid crystal displaypanel, and light input to a side surface of the second light guide plateis used for a first mode of the liquid crystal display panel.
 3. Thedisplay device as claimed in claim 1, wherein the liquid crystal displaypanel is driven in a first mode, when light input to a side surface ofthe second light guide plate progresses towards the first light guideplate through the upper surface of the second light guide plate havingthe second recessed patterns.
 4. The display device as claimed in claim1, wherein a brightness of light input to a side surface of the secondlight guide plate is different from a brightness of light input to theincident surface of the first light guide plate.
 5. The display deviceas claimed in claim 1, wherein the liquid crystal display panel isdriven in a second mode when light is not input to a side surface of thesecond light guide plate.
 6. The display device as claimed in claim 1,wherein both of the first and second light guide plates have one of aplanar profile and a wedge profile.
 7. The display device as claimed inclaim 6, wherein both of the first and second light guide plates havethe wedge profile, and the incident surface of the first light guideplate and an incident surface of the second light guide plate aredisposed to face each other with respect to middle portions of the firstand second light guide plates.
 8. The display device as claimed in claim6, wherein both of the first and second light guide plates have theplanar profile, and the incident surface of the first light guide plateand an incident surface of the second light guide plate are disposedtogether with respect to middle portions of the first and second lightguide plates.
 9. The display device as claimed in claim 1, furthercomprising a first light source disposed at a first polarizing plate ofthe first light guide plate and a second light source disposed at a sideof the second light guide plate.
 10. The display device as claimed inclaim 9, wherein a brightness of the second light source is 1.3˜1.5times more than that of the first light source when the liquid crystaldisplay panel is driven in a transparent mode.